Nickel-base alloy for use at elevated temperature



United States Patent Office 3,389,992 Patented June 25, 1968 3,389,992 NICKEL-BASE ALLOY FOR USE AT ELEVATED TEMPERATURE Stuart Walter Ker Shaw, Coldfield, and Reginald Massey Cook, Kings Heath, Birmingham, England, assignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 14, 1965, Ser. No. 496,145 Claims priority, application Great Britain, Oct. 20, 1964, 42,767/ 64 13 Claims. (Cl. 75171) The present invention relates to nickel alloys suitable for use under stress at high temperature and, more particularly, to nickel-base alloys of a special and controlled composition such that the alloys are especially adapted for use at very high temperatures, e.g., 1100 C., for example, as stator and rotor blades for gas turbine engines.

During the last twenty-five years or so, the metallurgical art has witnessed the achievement of tremendous strides in the property characteristics of alloys used in high temperature applications. This uninterrupted advance largely has been in response to the requirements brought about by new engineering designs in related fields, notably the aircraft industry. With emphasis on greater speeds and higher strength-to-weight ratios, factors usually attendant higher speeds and greater load-bearing capacities, there quite naturally has been an ever present need for im proved alloys. Put another way, whereas the art was contending with temperatures of about 650 C. (1200 F.) prior to, say, 1950 it is now concerned with problems associated with temperatures upwards of 1000 C. (1832 F.) or 1100 C. (2012 R). And the foreseeable future does not seem to indicate the arrestment of this trend.

In our US. Patent No. 3,166,413 we have described alloys capable of operating satisfactorily at temperatures of about 1000 C., the alloys broadly containing from 5% to chromium, 7% to 16% tungsten, up to 5% molybdenum, up to 4% columbium (niobium), the sum of the tungsten, molybdenum and columbium contents plus twothirds of the chromium content being from 17.5% to 20.5%, 2% to 8% aluminum, 0.03% to 0.3% carbon, up to 1% zirconium and up to 0.05% boron, the balance apart from impurities, being essentially nickel. It would be most desirable to substantially improve upon the metallurgical properties of such alloys, particularly the stressrupture characteristics thereof, and it is to this objective to which the present invention is directed.

It has now been found that the stress-rupture properties at temperatures above 1000 C. of alloys such as those above described, can be improved to a marked extent provided the chromium content thereof is especially controlled and the respective amounts of the other constituents are correlated in the manner hereinafter described.

It is an object of the present invention to provide a nickel-base alloy having improved stress-rupture characteristics at temperatures on the order of about 1100 C., particularly when subjected to relatively high stress.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates providing nickel-base alloys characterized by good stressrupture properties at exceptionally high temperatures, e.g., 1100 C., while under stress, the alloys containing (by weight), up to about 4% and preferably from 1% to 3.5% chromium, about 7% to 19.5% tungsten, up to 7% molybdenum, up to 4% columbium, the sum of the tungsten plus 1.2 times the molybdenum plus the columbium plus two thirds of chromium being from 16.5% to 22%, from 4.7% to 6.8% aluminum up to 22% cobalt, up to 0.5% carbon, up to 1.3% zirconium, up to 0.05 boron, the balance, apart from impurities, being nickel. The use of the expression balance or balance essentially in referring to the nickel content of the alloys, as will be understood by those skilled in the art, does not exclude the presence of other elements commonly present as incidental elements, e. g., deoxidizing and cleansing elements, and impurities normally associated therewith in small amounts which do not adversely affect the novel characteristics of the alloys. In this connection, the principal impurities that may be usually present are iron, silicon and manganese, and total amounts of these elements should be as low as possible and should not exceed 3%. Preferably the iron, silicon and manganese contents do not exceed 0.5%, 0.3% and 0.3%, respectively.

A particularly advantageous alloy composition is as follows: about 2% to 3.5% chromium, about 12% to 18.5% tungsten, up to 4% and preferably not more than 3% molybdenum, e.g., up to 2% molybdenum, from 0.2% to 2% columbium and most preferably from 0.2% to less than 1.5% columbium, the sum of 1.2 times the percent molybdenum plus the percent tungsten plus the percent columbium plus /3 the percent chromium being from 18% to 21%, about 5.25% to 6.25% aluminum, up to 16% and preferably from 5% to about 16% cobalt, from 0.05 to 0.3% carbon, up to 0.035% boron, about 0.1% to 1% zirconium and the balance essentially nickel.

The effect on the stress-rupture properties as a result of using chromium contents both within and without the invention is shown by the test results in Table I. The nominal composition (percent by weight) of the alloy base to which different chromium contents were added is as follows: 0.13% carbon, 18% tungsten, 1% columbium, 6% aluminum, 0.5% zirconium, with nickel constituting the balance. In Table I Alloys 1 to 4 are in accordance with the invention while Alloy 5 is not. The stress-rupture life in hours (hrs.) and percent tensile elongation (Elong) are reported in Table I, the test conditions being 1100 C. under a stress of 7 long tons per square inch (t.s.i.).

TABLE I Stress-Rupture Properties at 7 t.s.i./1,100 0. Alloy No. Cr (percent) Life Elong. (hrs.) (percent) 0 *20 2 49 9. l 3 58 ll. 0 4 23 5. 6 6 9 6. 1

*Estimated from tests at 1,070 C.

As reflected by Table I, the best properties are obtained when the chromium content is from 1 to 3.5%; however, if resistance to oxidation is of particular importance the chromium content is preferably at least 2%. The chromium content can be extended to 4% but as illustrated by Alloy 4, the stress-rupture life is considerably reduced.

The stress-rupture properties are also critically dependent upon the contents of tungsten, molybdenum and columbium and the effect of variations in the proportions of these constituents is shown in Table II. The base alloy (nominal) in which the above-mentioned three elements were varied contained 0.13% carbon, 3% chromium, 6% aluminum, 0.5% zirconium, the balance being nickel. All the alloys except those indicated by an asterisk are in accordance with the invention.

TABLE II Stress-Rupture Proper- Alloy Percent 12 ties at 7 t.s.i./1,100 C.

N 0. Mo+W+Cb Mo W Cb +2/3 Cr Lite (hrs.) Elong.

(percent) 2O 0 22 7 0 20 l. 0 23 1G 8. 2 0 18 0 20 24 10. 4 0 18 (l. 5 20. 5 52 13. 4 0 18 1. 0 21 58 11. 0 0 18 1. 5 21. 5 23 0 18 3. 0 23 11 8. 9 O 16 0. 5 18. 5 69 32. Z 2 16 0. 5 20. 9 45 19. 9 2 14 1. 0 19. 4 52 9. 9 2 14 1. 5 19. 9 49 0 12 1. 0 15 4 4 12 1. 5 20. 3 43 19. 8 6 12 0. 5 21. 7 231 9. 2 6 12 1. 5 22. 7 14 7. 7 2 10 0. 5 14. 9 5 4 8 0. 5 15. 3 5 6 8 1. 5 l8. 7 23 6. 4 6 6 0. 5 15. 7 12 12. 0 6 6 1. 5 16. 7 16 11.5

The results for Alloys 6 and 24 show the poor stressrupture properties obtained when the tungsten content is less than 7% or more than 19.5%, even though the value of the relationship is within the critical limits of 16.5% to 22%. Similarly, the poor results for Alloys 7, 11, 16, 19, 20, 21 and 23 show the need to comply with the relationship.

In addition, a comparison of Alloys 9, 12 and 13 with Alloy 18 and of Alloys 15 and 17 with Alloy 22 generally reflect the drop in properties as tungsten is replaced by molybdenum. For the longest life and maximum elongation, the molybdenum content should not exceed 4% and preferably should not be more than 3%, and most advantageously the alloys are substantially free from molybdenum.

Variation in the columbium content also has a marked effect on the properties. Thus, Alloy 9 with only 0 .5% columbium had more than double the life of the columbium-free but otherwise similar Alloy 8. However, increasing the columbium content above 1% causes stressrupture to fall again, and the elongation is also reduced. This is indicated, for example, by a comparison of Alloy 9 with Alloys 10 and 11 which were of the same composition except that Alloy 9 contained 0.5% columbium versus 1.5%. for Alloy 10 and 3% for Alloy 11, the latter alloy also being outside the above-described relationship. Preferably, therefore, the columbium content is from 0.2% to 2% and most advantageously the columbium content does not exceed 1% or 1.5%.

Tests on alloys with different aluminum contents have shown that the best stress-rupture properties are obtained with about 6% aluminum, the rupture lives tending to fall 011 with either more or less aluminum. This general effect is illustrated by the results in Table III, in which all the alloys except Alloy 28 are in accordance with the invention. The base alloy composition (except for aluminum, of course) was the same alloy base used in connection with Table I, the nominal chromium content being 3%.

TABLE III Stress-Rupture Properties at 10 While variation of the cobalt content in amounts up to 16% has little marked effect upon the stress-rupture lives of the alloys, if the highest elongation is required they should contain at least 5% of cobalt. As the cobalt content is increased above about 16%, the stress-rupture life falls and preferably, therefore, the cobalt content does not exceed 16%. These effects are illustrated by the results for the alloys in Table IV in which the columbium content was also varied. All the alloys of Table IV except Nos. 39, 40 and 41 are in accordance with the invention and the nominal base alloy composition (other than for the cobalt and columbium) was the same as given regarding Alloy 3, Table I.

TABLE IV Stress-rupture Properties at A110 00 Ch 7 t.s.i./1,100 O.

No (Percent) (Percent) Life (hrs.) Elong. (Percent) 0 0. 5 52 13. 4 0 1. 0 58 11. 0 O 1. 5 23 5 0. 5 58 17. 7 5 1. 0 52 14. 2 10 0. 5 45 14. 9 10 1. 0 62 18. 9 1O 1. 5 54 9. 5 15 0. 5 46 23. 3 15 1. 0 60 20. 9 20 0. 5 19 19. 3 20 1. 0 23 12. 9 20 1. 5 26 10. 4 3O 0. 5 12 3O 1. O 9 24. 3 30 1. 5 12 18. 0

Within the range 0.05% to 0.3%, carbon has little effect on the stress-rupture properties of the alloys. Above and below these limits the properties generally fall off.

On the other hand, however, the impact properties of the alloys at high temperatures are improved by utilizing low carbon contents, and for the greatest impact strength the carbon content should not exceed 0.05% and can even be less than 0.3%. When the carbon content is less than about 0.03%, the alloys should contain at least 0.01% boron for attaining optimum stress-rupture characteristics.

The effects of carbon content on the impact and stressrupture properties of the alloys are illustrated by the test results in Table V. The impact strengths were determined on unnotched bars 0.45 inch in diameter. Apart from the carbon and columbium contents given in Table V the alloys nominally combined 3% chromium, 10% cobalt, 18% tungsten, 6% aluminum, 0.5% zirconium, 0.02% boron and the balance nickel.

TABLE V 60 Impact Stress-rupture properties Percent strength at 7 t.s.i./1,100 C. Alloy No. at 850 C.

Cb (ft.-lbs.) Life (hrs.) Elong.

Percent) Zirconium and boron improve the stress-rupture lives of the alloys, and it is preferred that the alloys contain from 0.1% to 1.0% of zirconium. When boron is present, the quantities of zirconium and boron are preferably so correlated that the value of the expression Percent Zr+10 (Percent B) is from 0.1% to 1.2%. As the boron content is increased above 0.035%, the stress-rupture lives fall off again, and preferably the boron content does not exceed this amount.

The properties of various alloys containing different amounts of zirconium are set out in Table VI, in which all the alloys except No. 49 are in accordance with the invention, the alloy base otherwise being again the same as given in Table I, the nominal chromium content being 3%.

TABLE VI Zr Stress-rupture properties at 7 t.s.i./l,100 0. Alloy N (Percent) Life (hrs) Elong. (Percent) The castability of the alloys is greatly impaired by titanium, and this element must therefore not be present except as an impurity.

The alloys may be air-melted, but are preferably melted under vacuum. Whether or not they are vacuum-melted, the alloys are advantageously subjected to a vacuumrefining treatment comprising holding them in the molten state under high vacuum before casting the melt. It is preferred to hold the melt at a temperature of about 1400 C. to 1700 C. at not more than 100microns pressure for a period of at least about minutes and advantageously for 60 minutes or more. The duration of the treatment depends to some extent on the purity of the ingredients of the melt, a longer time being required when less pure ingredients are employed.

When making small castings, for example, turbine blades or stressrupture test-pieces, the alloys are preferably cast under vacuum, but when making large castings from a melt that has been produced or refined under vacuum it makes little difference to the properties obtained Whether casting is carried out in vacuum, inert gas or air. All the stress-rupture test results given in this specification were obtained on test-pieces machined from specimens cast under vacuum at 1600 C. from vacuum-melted material that had been vacuum-refined for at least 15 minutes at 1550 C. under a pressure of less than 1 micron.

Articles and parts cast from the alloys may be used in the as-cast condition for high-temperature service. If desired the alloys may be homogenized by heating in the temperature range 850 to 1250 C. before being put into service.

For use at temperatures above 1000 C. under conditions such as are encountered in gas turbine engines, involving both oxidation and sulphur attack, articles and parts made from the alloys are preferably provided with a protective coating, for example, of aluminum.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. For example, a small amount of tantalum is commonly associated with columbium in commercially available forms thereof. For instance, columbium is available as an alloy nominally consisting of 40% nickel and 60% columbium, but up to one tenth of the nominal columbium content is often tantalum. Thus, the alloys may contain such tantalum as introduced with the columbium, and when tantalum is present it is to be regarded as part of the columbium content. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A nickel-base alloy characterized by good stressrupture characteristics at elevated temperatures of the order of about 1100 C. while under relatively high stress, said alloy consisting essentially of about 1% to 3.5% chromium, about 7% to 19.5% tungsten, up to 4% molybdenum, about 0.2% to 2% columbium, the sum of the tungsten plus 1.2 times the molybdenum plus the columbium plus two-thirds the chromium being from 16.5% to 22%, about 4.7% to 6.8% aluminum, up to 16% cobalt, up to 0.3% carbon, about 0.1% to 1% zirconium, up to 0.06% boron, the sum of the zirconium plus ten times the boron being from 0.1% to 1.2%, and the balance essentially nickel.

2. The alloy as set forth in claim 1 wherein the molybdenum content does not exceed 2%.

3. The alloy as set forth in claim 2 wherein the columbium content is 0.2% to 1.5%.

4. The alloy as set forth in claim 3 in which the columbium content is from 0.2% to 1%.

5. The alloy as set forth in claim 3 wherein the cobalt content is from 5% to 16%.

6. The alloy as set forth in claim 5 in which the boron content is from 0.1% to 0.35% and carbon is present in an amount not exceeding 0.05%.

7. The alloy as set forth in claim 6 in which the chromium content is from 2% to 3.5% and the carbon does not exceed 0.03%.

8. A nickel-base alloy characterized by good stressrupture characteristics at elevated temperatures of the order of about 1100 C. while under relatively high stress, said alloy consisting essentially of 2% to 3.5% chromium, about 12% to 18.5% tungsten, up to 4% molybdenum, about 0.2 to 2% columbium, the sum of the tungsten plus 1.2 times the molybdenum plus the columbium plus twothirds the chromium being from 18% to 21%, about 5.25% to 6.25% aluminum, up to 16% cobalt, about 0.05% to 0.3% carbon, about 0.1% to 1% zirconium, up to 0.035% boron, the sum of the zirconium plus ten times the boron being from 0.1 to 1.2%, and the balance essentially nickel.

9. The alloy as set forth in claim 8 wherein the molybdenum content does not exceed 2%.

10. The alloy as set forth in claim 9 wherein the columbium content is from 0.2% to less than 1.5

11. The alloy as set forth in claim 10 wherein the cobalt content is from 5% to 16%.

12. A nickel-base alloy characterized by good stressrupture characteristics at elevated temperatures of the order of about 1100 C. while under relatively high stress, said alloy consisting essentially of up to 4% chromium, about 7% to 19.5% tungsten, up to 7% molybdenum, up to 4% columbium, the sum of the tungsten plus 1.2 times the molybdenum plus the columbium plus two-thirds the chromium being from about 16.5% to about 22%, about 4.7% to about 6.8% aluminum, up to 22% cobalt, up to 0.5% carbon, up to 1.3% zirconium, up to 0.5 boron, and the balance essentially nickel.

13. The alloy as set forth in claim 12 wherein the chromium content is from 1% to 3.5%.

References Cited UNITED STATES PATENTS 2,948,606 8/1960 Thielemann 171 3,166,413 1/1965 Shaw et al. 75-171 3,301,670 1/1967 Bie'oer 75-171 3,322,534 5/1967 Shaw et a1. 75171 HYLAND BIZOT, Primary Examiner.

RICHARD O. DEAN, Examiner.

g gg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No- 3,389,992 Bau July 25. 1969 Inventor(s) STUART WALTER KER SHAW and REGINALD MASSEY COOK It is certified that error appears in the above-identified'patent and that said Letters Patent are hereby corrected as shown below:

w Column 4, line 47, for "0.3%" read --0.03%--. Column 6, line 24, for "0.1% to 0.35%" read -0.01% to 0.035%-.

SIGNED AND SEALED EP 3 01959 Attest:

Edward 1m mach", Jr. gy m. Anesfing Officer sioner of Patents 

1. A NICKEL-BASE ALLOY CHARACTERIZED BY GOOD STRESSRUPTURE CHARACTERISTICS AT ELEVATED TEMPERATURES OF THE ORDER OF ABOUT 1100*C. WHILE UNDER RELATIVELY HIGH STRESS, SAID ALLOY CONSISTING ESSENTIALLY OF ABOUT 1% TO 3.5% CHROMIUM, ABOUT 7% TO 19.5% TUNGSTEN, UP TO 4% MOLYBEDENUM, ABOUT 0.2% TO 2% COLUMBIUM, THE SUM OF THE TUNGSTEN PLUS 1.2 TIMES THE MOLYBDENUM PLUS THE COLUMBIUM PLUS TWO-THIRDS THE CHROMIUM BEING FROM 16.5% TO 22%, ABOUT 4.7% TO 6.8% ALUMINUM, UP TO 16% COBALT, UP TO 0.3% CARBON, ABOUT 0.1% TO 1% ZIRCONIUM, UP TO 0.05% BORON, THE SUM OF THE ZIRCONIUM PLUS TEN TIMES THE BORON BEING FROM 0.1% TO 1.2% AND THE BALANCE ESSENTIALLY NICKEL. 